With ever increasing demands for miniaturization and higher operating speeds, semiconductor packages having a plurality of semiconductor chips, i.e., multi-chip modules (MCMs), are increasingly attractive in a variety of electronics. MCMs which contain more than one die can help minimize the system operational speed restrictions imposed by long printed circuit board connection traces by combining, for example, the processor, memory, and associated logic into a single package. In addition, MCMs decrease the interconnection length between IC chips thereby reducing signal delays and access times.
However, in certain applications (e.g., tire pressure monitoring systems (TPMS) for monitoring the pressure in automotive tires), it is desirable to have one chip, e.g., a sensor chip separate from other integrated circuit chips for reasons of functionality, reliability, safety, and/or manufacturability. TPMS typically include a sensor chip for sensing tire pressure and an application specific integrated circuit (ASIC) responsive to temperature and system battery voltage.
TMPS have been packaged in a variety of ways. WO 2005/038422 A1 discloses that components for a tire pressure monitoring system (TPMS) may be packaged on a common leadframe in which the ASIC is over-molded and rendered insensitive to the local environment, and the sensor chip is disposed in open cavity sealed with a cover having pressure transfer aperture. However, the sensor chip of this conventional TPMS is directly supported by the die pad of the leadframe. Since there is a significant difference between the sensor chip and the die pad in coefficient of thermal expansion (CTE), the sensor chip and the die pad expand and contract in different amounts along with temperature fluctuations from the environment to which the sensor chip is exposed. This causes warpage of the sensor chip thereby resulting in adverse influences that makes the sensor chip unable to sense tire pressure. Furthermore, the thermal stress due to CTE mismatch may result in delamination between the sensor chip and the die pad or chip cracking. Also, such differences in CTE could induce undesirable strains in the mechanical and electrical connections between the sensor chip and the leadframe.